Method and system for transmitting a multimedia stream

ABSTRACT

A method is described for transmitting a multimedia stream from a first end-terminal to a second end-terminal. The first and second end-terminal are connected to at least one gateway for enabling the multimedia stream to be transmitted from the first end-terminal to the second end-terminal. The method comprising the steps of: the first end-terminal inviting the gateway to set up a first multimedia session between the first end-terminal and the gateway, the first multimedia session being controlled by a first protocol; the gateway notifying—in response to the invitation—the second end-terminal of the pending invitation; the second end-terminal setting up—in response to the notification—a second multimedia session between the second end-terminal and the gateway, the second multimedia session being controlled by a second protocol; the gateway setting up—in response to the invitation—the first multimedia session; and transmitting a multimedia stream from the first end-terminal to the second end-terminal. The first protocol may be SIP, the second protocol may be RTSP.

FIELD OF THE INVENTION

The invention relates to a method and a system for transmitting amultimedia stream from a first terminal to a second terminal. Inparticular, the invention relates to a method and system fortransmitting a first multimedia stream from a first terminal andreceiving a second associated stream at a second terminal. The inventionfurther relates to a gateway and a device for use in such system.

BACKGROUND OF THE INVENTION

IP Multi-Media Subsystem (IMS) defined by the 3GPP and 3GPP2 standardsopen the door to a whole range of new multimedia services, such as Voiceover IP (VoIP) and IPTV. The IMS service architecture enables to combinemultimedia services of various types.

One type of services may enable viewers at home to participate real-timein a live TV show using e.g. a webcam at home. The multimedia streamsgenerated by the webcam are transported from the home-located user overan IP network to the TV studio using the Real-time Transport Protocol(RTP). In an IMS based architecture such multimedia streaming sessionsbetween clients are set up using the Session Initiation Protocol (SIP),whereas the Real Time Streaming Protocol (RTSP) is typically used forstreaming multimedia content from a server to a client.

Systems that provide an interface between SIP and RTSP domains, usuallyreferred to as SIP-RTSP gateways, are known in the art. Within ETSITISPAN Standardization (WI2048, TS 182 027) an architecture is proposedin which a terminal, comprised in a device such as for example a set-topbox, a personal computer, a personal digital assistant (PDA) or a mobiletelephone with multi-media capabilities, uses SIP to set up a multimediasession with a selected content provider. After establishment of thesession, RTSP is used to select, retrieve and control the streamedcontent. Further, the University of Colombia (Kundan Singh and HenningSchulzrinne, “Unified Messaging using SIP and RTSP”, IP Telecom ServicesWorkshop, September 2000, Atlanta, Ga., US) has developed a SIP-RTSPGateway for multimedia unified messaging.

These systems use SIP and RTSP clients at the user side and SIP clientsand RTSP servers in the network, thereby enabling a user to initiate theset up multimedia session in which multimedia content is streamed fromthe RTSP servers to the user.

Another gateway system that may be used to stream multimedia betweendifferent protocol domains is described in TAKEI K ET AL “Design ofgateway system between different signaling protocols of the multimediasession on the internet” INFORMATION NETWORKING, 2001. PROCEEDINGS.15^(TH) INTERNATIONALCONFERENCE ON 31 JANUARY-2 FEBRUARY, PISCATAWAY,N.J., USA, IEEE, 2001, PAGES 297-302, ISBN: 0-7695-0951-7/01. Thissystem is used to interwork the SIP and the H323 protocol domains. Bothprotocols are peer-to-peer type protocols and allow for bidirectionalset-up/initiation of sessions.

One problem related to these known systems is that they do not provideall the functionality needed for the above mentioned services, whichrequire the user to initiate the set up a multimedia session such thatuser-generated content is streamed from the user (the transmitting-end)to the studio (the receiving-end), whereby the studio may want tocontrol the stream of user generated content. A known protocol forcontrolling a stream is RTSP, whereby the receiving-end, with RTSPclient functionality, may be able to pause, or forward or backward astream, or play a stream at a different speed. If the transmitting-endon the other hand is only capable of using the SIP protocol for settingup and maintaining the multimedia streaming session, the mentionedservices cannot be realized with the known prior art systems, since theSIP protocol does not provide the means for controlling a stream in theway that for instance the RTSP protocol is capable of.

Another problem related to the streaming of multimedia, that may arisewith prior art systems, is that when the receiving-end is only equippedwith client functionality of a client-server type of protocol forreceiving multimedia, it may only be capable of initiating a multimediasession. If the transmitting-end, using for example a peer-to-peer typeof protocol, such as the SIP protocol, wants to initiate a multimediastreaming session, the receiving-end is not capable to respond to suchan invitation. Prior-art systems, such as the known SIP-RTSP gatewaysand the known SIP-H323 gateways do not provide a solution for thisproblem.

A variety of additional problems may arise with prior art systems, whenthe user generated multimedia has to be streamed to a multiple ofreceiving-ends. These receiving-ends may all have different capabilitiesor preferences when it comes to receiving a multimedia stream. Onereceiving-end may want to receive a live stream, whereas the other maywant to be able to control the stream as described above. Additionallythese preferences and capabilities, as well as the network addresses ofthe receiving-ends, may not be known to the transmitting-end.

SUMMARY OF THE INVENTION

It is an object of the invention to reduce or eliminate at least one ofthe drawbacks known in the prior art and to provide a method and systemfor transmitting a first multimedia stream from a first terminal andreceiving a second associated multimedia stream at a second terminal.

In an embodiment the first and second terminal are connected to at leastone gateway for enabling the transmission of the first multimedia streamand the receiving of the second associated stream. The method comprisesthe steps of:

-   -   initiating the exchange of first multimedia session information        between the first terminal and the gateway, using a first        protocol;    -   providing a trigger to the second terminal to initiate the        exchange of second multimedia session information between the        second terminal and the gateway, using a second protocol;    -   in response to the providing of the trigger, the second terminal        initiating the exchange of second multimedia session information        between the second terminal and the gateway, using a third        protocol, the third protocol being different from the second        protocol;    -   transmitting a first multimedia stream from the first terminal        and receiving a second associated multimedia stream at the        second terminal.        The method thus allows the user of a first terminal to transmit        a multimedia stream of real-time user-generated content to a        second terminal, whereby the first terminal uses a different        multimedia protocol to set up a multimedia stream as that the        second terminal uses to receive the associated multimedia        stream.

In the method according to the embodiment a gateway is capable ofconnecting a first terminal supporting a first protocol, e.g. SIP, to asecond terminal supporting a different (third) protocol, e.g. RTSP.Towards the first terminal, i.e. the (originating) SIP client at theuser side, the gateway acts as (terminating) SIP client. The gatewayexchanges information about the specifications of the first multimediasession with the first terminal. In the first multimedia session amultimedia stream is transmitted from the first terminal. Towards thesecond terminal, i.e. the RTSP client, the gateway acts as RTSP serveron behalf of the user, whereby the second terminal uses RTSP forexchanging information about the specifications of the second multimediasession with the gateway. In the second multimedia session a multimediastream is received by the second terminal.

The second terminal is triggered, using a second protocol that isdifferent from the protocol used by the second terminal to exchangesecond multimedia session information, informing the second terminal ofthe availability of a new multimedia stream and activating the RTSPclient to connect to the RTSP server function of the gateway. Optionallythe activation of the RTSP client may occur only after approval of theuser of the second terminal. The approval step is then simply part ofthe fully automated process.

The gateway acts both as a SIP client and RTSP server and may provide atrigger to the second terminal for connecting the second terminal to thegateway. The invention is based on the idea that the trigger is providedusing a different protocol then the protocol used by the second terminalto arrange the receipt of multimedia. This idea is based on the insightthat some protocols are only capable of initiating a multimedia sessionin one direction. The trigger (message) ensures that SIP clients fromthe user and RTSP clients from the studio can be connected in order toenable user-generated content to be transmitted from the first terminalto the second terminal.

In a further embodiment of the method according to the invention, theexchange of first multimedia session information comprises the providingto the first terminal of at least part of the second multimedia sessioninformation and whereby transmitting of the first multimedia stream fromthe first terminal is started in response to said providing. This hasthe advantage of providing additional flexibility to the method. It isno longer the gateway that supplies preconfigured specifications of bothrelated multimedia sessions to the terminals involved in thetransmitting and receiving of the stream, but the gateway may use(requested by) settings from the second receiving terminal, and supplythese to the first, transmitting, terminal. Vice versa, and for the samebenefit, the gateway may use (requested by) settings from the firsttransmitting terminal, and supply these to the second, receiving,terminal. In both situations the transmitting, respectively receiving ofmultimedia streams may only start after the exchange of these settings.

In an embodiment of the method, the first protocol is a peer to peertype protocol, preferably the Session Initiation Protocol (SIP). Theadvantage of the peer-to-peer protocol is that both sides may initiatethe set-up of a streaming session. So in the invention, it may be thefirst terminal offering a multimedia stream or it may be the gatewayfirst requesting the first terminal to offer a multimedia stream. TheSIP protocol is a very commonly used protocol in multimedia sessions,and therefore a lot of devices and network architecture support thisprotocol.

In a further embodiment of the method the third protocol is aclient-server type protocol, preferably the Real Time Streaming Protocol(RTSP). Typically a client-server type of protocol is a protocol that isdesigned to support only one way initiation of the set up of amultimedia session. Only the client can typically initiate the set-up.Therefore the invention is advantageously used when the second receivingterminal has only client capabilities of such a protocol and thereforeis unable to receive an invitation via such a protocol. The use of theRTSP protocol, may be advantageous, when the receiving second terminalwants to control the incoming stream and use the special control optionsof this protocol.

In a further embodiment of the method, the step of providing a triggerto the second terminal is initiated by the gateway. Having the gatewayand not for example the first terminal provide the trigger, may beadvantageous when the first terminal does not have the right triggercapabilities, does not know how to reach the second terminal, and incase of a multiple of receiving terminals, that need to be reached.

In yet a further embodiment of the method, the trigger comprises anetwork address, preferably an URI or URI reference, of the gateway.This may be advantageous, if the second terminal is not configured witha default address, or the default (proxy) address normally used forreceiving multimedia streams is not applicable.

In another embodiment of the method, the exchange of first multimediasession information comprises the provisioning of an identifier of thesecond terminal to the gateway. This may be advantageous, if it is thegateway that provides the trigger to the second terminal. In thatsituation, it is the gateway that needs to be able to identify theaddress of the second terminal to be reached.

In a further embodiment of the method, the method comprises the additionstep of resolving the identifier of the second terminal into a networkaddress, before provisioning of the trigger to the second terminal. Thismay be the situation, when the trigger is sent by the gateway and theidentifier does not comprise of a network address of the secondterminal. The identifier may be a closed user group ID, in which caseall network addresses of all receiving terminals need to be identifiedfirst.

In another embodiment according to the method, the first and the secondprotocol are identical. This simplifies the implementation of theinvention. A situation like this may occur when the receiving terminalhas both RTSP and SIP client capabilities. The trigger may then beprovided using the SIP protocol, whereas the initiation and set up ofthe receipt of the multimedia stream may be done, using the RTSP client,thus enabling control functionalities (trickplay) that SIP lacks.

In another embodiment of the method, the second associated multimediastream is a multicast stream. This may be advantageous when a multipleof receiving terminals may be offered the live multimedia stream. Theymay, after being provided with the trigger, and having received amulticast address from the gateway in the exchange of second multimediasession information, use IGMP to sign-up for the multicast.

In a further embodiment of the method the first multimedia stream is amulticast stream. This is advantageous when the first transmittingterminal has (received) a multicast address it can use to multicast itsmulti-media stream.

In yet a further embodiment of the method, the first multimedia streamis the same multimedia stream as the second associated multimediastream. In this case the (live) content may also be receivedlive/without any substantial delay from the transmitting first terminal.For enabling additional trickplay (control) functionality, thetransmitted multimedia stream needs to be streamed and buffered first toa location under the control of a multimedia server such as a RTSPserver, before it is retransmitted as a second associated stream to asecond terminal. The additional control functions (e.g. forward,backward, pause) may then be exerted on this second associated stream.

In another embodiment of the method, the first terminal and the gatewayare both comprised in the same device and the first protocol is aninternal protocol. This may be an advantageous implementation when thenetwork (or studio/receiving-end) does not have the gatewayfunctionality according to the invention. Preferably this situation mayoccur when there exist a one-to-one relationship between thetransmitting and receiving terminal, and both terminals are comprised inmobile devices.

In an aspect the invention relates to a system for transmitting amultimedia stream from a first terminal and receiving an associatedsecond multimedia stream at a second terminal, wherein the systemcomprises:

a first terminal and second terminal connected to at least one gateway,

wherein the first terminal comprises (i) means for exchanging firstmultimedia session information with the gateway, using a first protocol,and (ii) means for transmitting a first multimedia stream;

wherein the gateway or first terminal comprises (iii) means fortriggering a second terminal, using a second protocol, —to initiate theexchange of second multimedia session information between the secondterminal and the gateway, using a third protocol,

wherein the second terminal comprises (iv) means for receiving atrigger, using a second protocol, and v) means for initiating theexchange of second multimedia session information with the gateway inresponse to said trigger, using a third protocol, and (vi) means forreceiving a second multimedia stream, associated with the firstmultimedia stream;

In a further embodiment of the system according to the invention, thegateway further comprises means for associating the first multimediasession information to the second multimedia session information. Thismay be advantageous, when the gateway does not have a defaultconfiguration, how to instruct transmitting and receiving terminals, butwhen a more flexible arrangement is required, whereby the settingrequests and capabilities of the terminals involved is taken intoaccount when setting up the multi-media sessions.

Yet another aspect of the invention relates to a gateway configured foruse in the system according to the invention, wherein the gatewaycomprises:

-   -   means for exchanging first multimedia session information with a        first terminal, using a first protocol,    -   means for triggering the second terminal, the trigger being        provided using a second protocol, in response to which the        second terminal is able to initiate the exchange of second        multimedia session information with the gateway, and    -   means for exchanging second multimedia session information with        the second terminal, using the third protocol, the third        protocol being different from the first protocol.

In a further embodiment of the gateway according to the invention, thegateway further comprises means to associate the first multimediasession information and the second multimedia session information witheach other

In yet a further embodiment of the gateway according to the invention,the gateway comprises SIP client functionality and RTSP serverfunctionality.

In yet a further embodiment of the gateway according to the invention,the gateway is embedded in an IMS network architecture, wherein thefirst protocol is SIP, the third protocol is RTSP, and wherein

-   -   means for exchanging first multimedia session information are        part of the Service Control Function within IMS    -   means for the triggering of the second terminal are part of the        Service Control Function within IMS    -   means for exchanging second multimedia session information are        part of the Media Function within IMS

IMS is an architecture that is becoming more and more popular amongoperators to be used for the provisioning of multimedia services to itscustomers. The distributed gateway according to an embodiment of theinvention, is particular advantageous, because it may be implementedusing standard(ized) components and functionalities already present inthe IMS architecture.

In one embodiment of the invention a first terminal is connected to asecond terminal. Further, the first and second terminal are connected toat least one gateway for enabling the multimedia stream to betransmitted from the first terminal to the second terminal. The methodcomprises the steps of: (i) the first terminal inviting the gateway toset up a first multimedia session between the first terminal and thegateway, the first multimedia session being controlled by a firstprotocol; (ii) the gateway notifying—in response to the invitation—thesecond terminal of the pending invitation; (iii) the second terminalsetting up—in response to the notification—a second multimedia sessionbetween the second terminal and the gateway, the second multimediasession being controlled by a second protocol; (iv) the gateway settingup—in response to the invitation—the first multimedia session; and (v)transmitting a multimedia stream from the first terminal to the secondterminal.

The method according to the embodiment thus allows the user of a firstterminal, which uses a first multimedia protocol, to stream real-timeuser-generated content to a second terminal, which uses a secondmultimedia protocol, where both the first and second terminal act as aclient.

In the method according to the embodiment a gateway is capable ofconnecting a first terminal supporting a first protocol, e.g. SIP, to asecond terminal supporting a second protocol, e.g. RTSP. Towards thefirst terminal, i.e. the (originating) SIP client at the user side, thegateway acts as (terminating) SIP client. The gateway confirms that itis able to receive the multimedia session from the user and providesfirst terminal with multimedia session information. Towards the secondterminal, i.e. the RTSP client, the gateway acts as RTSP server onbehalf of the user, whereby the second terminal uses RTSP for sessioncontrol.

The gateway informs the second terminal that an incoming session ispending and notifies the RTSP client to connect to the RTSP serverfunction of the gateway.

The gateway thus acts as a server for both SIP and RTSP and uses anotification message for connecting to the second terminal RTSP client.This message acts as a trigger message and ensures that legacy SIPclients from the user and RTSP clients from the studio can be connectedin order to enable user-generated content to be transmitted from thefirst terminal to the second terminal.

In one embodiment the first protocol is the Session Initiation Protocol(SIP). In a further embodiment the first terminal transmits an SIPINVITE to the gateway.

In a further embodiment the second protocol is the Real Time StreamingProtocol (RTSP).

In yet another embodiment the gateway transmits a notification messageto the second terminal in response to invitation of the first terminal,in order to activate the second terminal to set up the second multimediasession between the second terminal and the gateway.

In one embodiment the method comprises the steps of: —the first terminaltransmitting first multimedia session information to the gateway; —thegateway transmitting the first multimedia session information to thesecond terminal.

In another embodiment the method comprises the steps of: —the secondterminal transmitting second multimedia session information to thegateway; —the gateway transmitting the second multimedia sessioninformation to the first terminal. The first multimedia sessioninformation and/or second multimedia session information is in a furtherembodiment transmitted using the Session Description Protocol (SDP).

In yet another embodiment the first terminal comprises a SIP clientand/or the second terminal comprises an RTSP client.

In a further embodiment the invention relates to a method fortransmitting a multimedia stream from a first terminal to a secondterminal, wherein the first and second terminal are connected to a firstand a second gateway respectively. The gateways are capable of settingup a multimedia session between the first and second terminal. Themethod comprises the steps of: (i) the first gateway preparing the firstterminal for setting up a multimedia session with the second terminal,wherein a first protocol is used for the preparation of the firstterminal; (ii) the first gateway inviting the second gateway to set upthe multimedia session between the first terminal and the secondterminal, the multimedia session being set up by a second protocol;(iii) the second gateway notifying—in response to the invitation—thesecond terminal to prepare the multimedia session with the firstterminal wherein the first protocol is used for preparation of thesecond terminal; (iv) setting up—in response to the invitation—amultimedia session between first terminal and the second terminal; and(v) transmitting a multimedia stream from the first terminal to thesecond terminal.

In this embodiment the purpose of the first SIP-RTSP gateway at the userlocation and the second SIP-RTSP gateway at the studio location is toexchange the correct RTP information (IP addresses, port number, SDPsession description, etc.) between the legacy SIP and RTSP functions.This allows the RTP stream to be set-up and controlled by the SIPsession and enables the user to trigger the TV studio to retrieve thestreamed user-generated content. The RTSP protocol may be used tocontrol the RTP stream.

In one embodiment the first protocol may be the Real Time StreamingProtocol (RTSP). In another embodiment the second protocol is theSession Initiation Protocol (SIP).

In a further embodiment the second gateway transmits a notificationmessage to the second terminal in response to the invitation of thefirst gateway, in order to activate the second terminal to set up themultimedia session between the first terminal and the second terminal.

In one embodiment the method further comprises the steps of: —the firstgateway receiving first multimedia session information from the firstterminal using the SDP protocol encapsulated in the first protocol andtransmitting the first multimedia session information to the secondgateway using the SPD protocol encapsulated in the second protocol;and—the second gateway receiving the first multimedia sessioninformation from the first gateway and transmitting the first multimediasession information to the second terminal using the SDP protocolencapsulated in the first protocol.

In another embodiment the method further comprises the steps of: —thesecond gateway receiving in response to the receipt of the first multimedia session information second multimedia session information from thesecond terminal using the SDP protocol encapsulated in the firstprotocol and transmitting the second multimedia session information tothe first gateway using the SPD protocol encapsulated in the secondprotocol; —the second gateway receiving the second multimedia sessioninformation from the second gateway and transmitting the secondmultimedia session information to the first terminal using the SDPprotocol encapsulated in the first protocol.

The transmission of the multimedia stream from the first terminal to thesecond terminal is in one embodiment controlled by the RTSP protocol.

In a further embodiment the first terminal comprises a RTSP serverconnected to the first gateway and/or the second terminal comprises anRTSP client connected to the second gateway.

In a further aspect the invention relates to a system for transmitting amultimedia stream from a first terminal to a second terminal. In oneembodiment the system comprises: a first terminal and second terminalconnected to at least one gateway, wherein the first terminal comprises(i) means for inviting the gateway to set up a first multimedia sessionwith the first terminal, wherein the first multimedia session iscontrolled by a first protocol and (ii) means for transmitting amultimedia stream in the first multimedia session to the gateway; andwherein the gateway comprises (iii) means for notifying—in response tothe invitation of the first terminal—to set up a second multimediasession between the gateway and the second terminal, the secondmultimedia session being controlled by a second protocol, (iv) means forsetting up—in response to the invitation—the first multimedia sessionand (v) means for transmitting a multimedia stream to the secondterminal.

In a further embodiment a system is provided for transmitting amultimedia stream from a first terminal to a second terminal. The systemcomprises a first terminal and second terminal connected to a first anda second gateway respectively. The gateways are capable of setting up amultimedia session between the first and second terminal, wherein thefirst gateway comprises: (i) means for preparing the first terminal forsetting up a multimedia session with the second terminal wherein a firstprotocol is used for the preparation of the first terminal; (ii) meansfor inviting the second gateway to set up the multimedia session betweenthe first terminal, the multimedia session being set up using a secondprotocol;

wherein the second gateway comprises: (iii) means for notifying thesecond terminal—in response to the invitation—to prepare the multimediasession with the first terminal, wherein the first protocol is used forthe preparation of the second terminal and (iv) means for setting up—inresponse to the invitation—a multimedia session between first terminaland the second terminal.

In yet a further aspect the invention relates to a device comprising afirst terminal configured for use in the method according to theinvention, the device further comprising a gateway according to theinvention. This may be advantageous when the (operator) network does notcomprise or support a gateway according to the invention. The device mayfor instance be a first mobile device wanting to offer a live stream toa home computer reachable via the internet.

In another aspect of the invention a device is claimed, comprising asecond terminal configured for use in the method according to theinvention, the second terminal comprising:

-   -   means for receiving a trigger, provided under the use of a        second protocol    -   means for initiating the exchange of second multimedia session        information with the gateway, in response to the providing of        the trigger to the second terminal, said initiating and exchange        executed under the use of a third protocol, said third protocol        being different from said second protocol.    -   means for receiving a second multimedia stream associated to a        first multimedia stream

Preferably this device is configured in such a way that the secondterminal comprises a RTSP client and the third protocol used to initiatethe exchange of second multimedia stream session information, is theRTSP protocol. This has the advantage that this device may now be ableto control the receipt of a multimedia stream and thereby use theavailable trick play functionality provided by the RTSP protocol.

In a further aspect the invention also relates to a computer programproduct comprising software code portions configured for, when run inthe memory of a terminal or gateway, executing the method stepsaccording to the invention.

The invention will be further illustrated with reference to the attacheddrawing, which schematically show embodiments according to theinvention. It will be understood that the invention is not in any wayrestricted to these specific embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary system in which the present inventionmay be used.

FIG. 2 depicts a simplified exemplary flow of information using the SIPprotocol.

FIG. 3 depicts an exemplary flow of information using the RTSP protocol.

FIG. 4 depicts an exemplary embodiment of the invention.

FIG. 5 a depicts the flow of information between a SIP client, aSIP-RTSP gateway and a RTSP client in an exemplary embodiment of theinvention.

FIG. 5 b depicts the flow of information between a SIP client, aSIP-RTSP gateway and a RTSP client in another exemplary embodiment ofthe invention.

FIG. 5 c depicts the flow of information between a SIP client, aSIP-RTSP gateway and a RTSP client in an exemplary embodiment of theinvention, whereby the first terminal and the gateway are both comprisedin a mobile device

FIG. 6 depicts an IMS architecture configured for use in the invention.

FIG. 7 depicts the flow of information in an exemplary IMS architectureconfigured for use in the invention.

DETAILED DESCRIPTION

FIG. 1 illustrates an exemplary system in which the present inventionmay be used. At the home-location a first terminal 1, e.g. comprised ina set-top box, is connected to display device, e.g. a television.Further, the first terminal receives a TV signal 2, which is broadcastedby the television studio and which comprises a program providing livemultimedia participation of home-located user. In one embodiment themultimedia participation of the user may be realized using e.g. aweb-cam 3 connected to the terminal. The multimedia stream 4 generatedby the web-cam is streamed over an IP network 5 to a second terminal 6located at the TV studio. At the TV studio the second terminal 6receives the user-generated multimedia stream 4. This way a live videofeed from the user to the studio may be provided.

Such a service requires (i) a home-located user to be able to set up amultimedia session between the home-located, first terminal 1 and thesecond terminal 6 located at the studio, wherein the multimedia sessionenables the streaming of user-generated multimedia content 4 to thestudio, and (ii) to enable the studio to control (e.g. play, pause,stop) the multimedia stream sent by the home-located terminal.

It is understood that the system at the home location allowingmultimedia participation as described in connection with FIG. 1 may berealized in various alternative ways. Those skilled in the art willunderstand that the first terminal 1, the display device and the web-cammay be for instance integrated in one device such as a personalcomputer, a digital assistant (PDA), a mobile telephone with multi-mediacapabilities. Similarly, the system at the studio may for example be amedia server comprising the second terminal, wherein the second terminalcomprises a RTSP client for multimedia stream retrieval. Alternatively,the second terminal may be located in a mixer or a transcoder andconfigured for multimedia stream adaptation.

In a further variant, the second terminal may be part of device, that islocated at another (home) location, and may be used for user-to-usermultimedia stream transmission. The device comprising the secondterminal may be a dedicated Set-Top Box (STB), a personal computer ormobile phone containing media player software.

The first terminal may be regarded as a functional unit in a device, ora device capable of managing (initiating, negotiating, monitoring andcontrolling) the transmission of a multimedia stream. Similarly, thesecond terminal may be regarded as a functional unit in a device, or adevice capable of managing (initiating, negotiating, monitoring andcontrolling) the receipt of a multimedia stream.

In an IMS architecture the SIP protocol is used to set up and/ornegotiate a multimedia session between two SIP clients e.g. two IPphones. Here, the term client may indicate a certain capability of adevice or terminal. For example a SIP client may refer to a deviceconfigured for using the SIP protocol or to a terminal having SIPcapability.

An exemplary flow using the SIP protocol is depicted in FIG. 2.Typically a first SIP client sends a SIP INVITE 7 to the second SIPclient, which in return accepts the invitation by transmitting a SIP 200OK 8 message to the first SIP client. Both messages may carryinformation about the multimedia session. This information is exchangedusing the Session Description Protocol (SDP), which may be encapsulatedin the SIP protocol. The multimedia session information may includeamongst others IP addresses, port numbers for the RTP streams, the typeof media (voice, audio, video, etc.) and codec information. Thereafter,multimedia may be streamed between the SIP clients using the RTPprotocol 9.

SIP however is designed for setting up and supporting interactive mediasessions. Although SIP also provides a form of aggregate streamingcontrol (i.e. the ability to control multiple streams from differentlocations with one control session), it does not provide for anefficient control as provided by the RTSP protocol used in streamingapplications such as Video on Demand (VoD). RTSP allows a client toremotely control a streaming media (RTSP) server by issuing VCR-likecommands e.g. play, pause, stop, skip forward, skip backward etc. andallows time-based access to files on a server. Moreover, legacyequipment may require the use of RTSP, since legacy equipment may not beprovided with a SIP client.

FIG. 3 schematically depicts an exemplary flow using the RTSP protocol.In setting up and controlling a RTSP multimedia session between an RTSPclient and an RTSP server, standard RTSP messages 10 (OPTIONS, DESCRIBE,SETUP, PLAY) are exchanged between the client and the server in order toprovide both sides with information required for an RTSP session. Theway the RTSP protocol is designed to operate, it is always the RTSPclient and not RTSP server that initiates the set up of such a session.Similar to SIP, RTSP session information is exchanged using the SessionDescription Protocol (SDP), which may be encapsulated in the RTSPprotocol. Once the session is set up, multimedia may be streamed fromthe server to the client 11, using the RTP protocol, wherein RTSP allowsthe client to control the streaming.

FIG. 4 depicts a schematic view of a system representing an exemplaryembodiment according to the invention. In this embodiment a home locatedfirst terminal 12 comprises a SIP client 13, which is capable to set upa SIP session 14 with an SIP-RTSP gateway 15. The SIP-RTSP gateway maybe located in a device that may also comprise the second terminal 16 atthe TV studio. The second terminal 16 comprises a RTSP client.

Towards the (originating) SIP client of the first terminal at the userside, the gateway acts as a (terminating) SIP client. The gatewayconfirms that it is able to receive the multimedia session from thefirst terminal and informs the first terminal at the user side on thesession details and the RTP port number. This first multimedia streamsession information may be exchanged using the SDP protocol, which maybe encapsulated in the SIP messages.

The gateway may further be capable of resolving an identifier receivedfrom the first terminal, used to identify the second terminal, into anetwork address of the second terminal. The resolution process may beperformed by the gateway or under the control of the gateway by anothermodule. The identifier may already be a suitable network address of thesecond terminal, in case of which the resolving is not required.

In response to the initiation of the exchange of first multimedia streamsession information, after being provided with a suitable networkaddress, the gateway may send a trigger message to the second terminal.The trigger message instructs the RTSP client to initiate an RTSPsession with the gateway. The gateway does not have to send the triggeritself, but may also instruct another module (such as a Short MessageService Center SMSC) to do so on its behalf.

Hence, towards the second terminal comprising the RTSP client 18, theSIP-RTSP gateway acts as an RTSP server, thereby allowing the RTSPclient to have RTSP session control over the RTP stream 19, which istransmitted from the first terminal (SIP client) and received as anassociated second multimedia stream at the second terminal (comprisingthe RTSP client).

The first multimedia stream may be the same multimedia stream as thesecond associated multimedia stream. In that case content is streameddirectly from the first to the second terminal. The transmitted firststream is not buffered under the control of a RTSP server before beingfurther transmitted as a second associated stream to the secondterminal. This has the advantage that the content is being presented in‘live modus’ to the second terminal. In this modus the trickplayfunctionalities (pause, fast forward etc.) of the RTSP client can not beused to control the stream.

FIG. 5( a) illustrates an exemplary embodiment of the flow ofinformation between the SIP client (comprised in the first terminal),the SIP-RTSP gateway and the RTSP client (comprised in the secondterminal). In a first step 20 the exchange of first multimedia streamsession information (SIP session) is initiated by the SIP client in thefirst terminal, which sends an SIP INVITE to the gateway indicating thatit wants to stream a first multimedia stream to the second terminal. Infurther variants, the first terminal may use another protocol toinitiate the exchange of first multimedia stream session information,such as H.323 or MPEG-4 Delivery Multimedia Integration Framework (DMIF)Default Signaling Protocol (DDSP).

In a second step 21 the gateway accepts the invitation and in response,provides the second terminal with a trigger to start an RTSP sessionwith the SIP-RTSP gateway. Optionally, the gateway may first need toresolve an identifier of the second terminal transmitted by the SIPclient in the first terminal, before it provides the trigger. Theresolving process to obtain the network address of the second terminalmay include a DNS, ENUM or other database query.

The gateway may add extra information to the trigger, such as a gatewaygenerated identifier, that can be used by the gateway to associate theincoming RTSP request from the second terminal (the RTSP request beingpart of the exchange of second multimedia stream session information)with the SIP session. The information in the trigger may be included inan RTSP URI.

The trigger may have the form of a trigger message, for example a SIPcontent indirection request (RFC 4483), a Short Message Service (SMS)message, or an Unstructured Supplementary Service Data (USSD) message.Further, the trigger message may be passed to the RTSP client using aproprietary application programming interface (API) or a controlinterface on the RTSP client, for example a Web Service interface usingSOAP, a Remote Procedure Call (RPC), or a telnet interface. Suchinterfaces may simulate a “manual user input” requesting a multimediastream.

The incoming trigger message may be interpreted by the trigger protocolstack (for example an SOAP stack or RPC stack) which may be configuredto instruct the RTSP client to request a multimedia stream or instructanother module to do so. Alternatively, the second terminal may useanother protocol to request a multimedia stream, such as Microsoft MediaServer protocol MMS, or Hypertext Transfer Protocol HTTP.

Thereafter, in a third step 22, the gateway handles the exchange ofsecond multimedia session information with the RTSP client comprised inthe second terminal, through transmitting the SDP information to theRTSP client and retrieving from the RTSP client the correct RTP port towhich the RTP stream should be sent to. During this exchange the gatewaygive instructions to the RTSP client, including for example the RTP portnumber that should be used for receiving the (second associated)multimedia stream or for example a multicast—or other address where thestream can be retrieved from.

In a fourth step 23, the gateway confirms the SIP session to the SIPclient using a SIP 200 OK message and provides the SIP client with theRTP port number, to be used for transmitting the first multimedia streamand confirms the SDP information. Finally, in the fifth and last step24, the first terminal starts streaming the RTP multimedia stream to thesecond terminal.

The termination of the combined SIP/RTSP session (not depicted in FIG.5( a)) may be handled in a similar way as the initiation of such sessiondescribed above. If the SIP client (of the first terminal) indicatesthat it wants to terminate the session, the gateway may translate an SIPBYE message into an RTSP REDIRECT message (without location header). TheRTSP REDIRECT message can be found in a draft of an updated RTSP version(see Internet draft RFC 2326 version 16 of the Real Time StreamingProtocol 2.0 dated 19 Nov. 2007 by Schulzrinne et al). If the RTSPclient (of the second terminal) indicates that it wants to terminate thesession, the gateway translates an RTSP TEARDOWN message into a SIP BYEmessage (which is then subsequently to be sent to the SIP clientcomprised in the first terminal)

In a further embodiment the streaming of multimedia may be firstinitiated by the gateway. In that case the gateway provides the RTSPclient comprised in the second terminal with the trigger message andinvites through its own SIP client functionality the SIP client of thefirst terminal to set up a SIP session. The flow of information betweenthe SIP client, the gateway and the RTSP client is schematicallydepicted in FIG. 5( b).

In yet a further embodiment the gateway may be located in the firstterminal. In that case the first protocol, used for the exchange offirst multimedia stream session information may just be an internalprotocol. The session may then be triggered by a stimulus of the userinterface of the first terminal. This scheme is schematically depictedin FIG. 5( c), wherein the first terminal may be comprised in a mobiledevice. Alternatively, the stimulus received by the first terminal mayalso come from an external source. In that case for example an SMSmessage received by the mobile device may trigger a session.

FIG. 6 depicts an implementation of the invention in an IMS-based IPTVarchitecture as defined by ETSI TISPAN. The architecture may for examplebe used for a scenario, wherein a first subscriber of an IMS based(user-generated) content service, commanding a first terminal (UE1 601),wants to stream his multimedia stream to a second subscriber, commandinga second terminal (UE2 602).

In this embodiment the gateway according to the invention is of thedistributed type, wherein the exchange of first multimedia streamsession information with the UE1 is typically handled by the ServiceControl Function (SCF 603) and the exchange of second multimedia streamsession information with the UE2 is handled by the Media Function (MF605). The provisioning of the trigger to the UE2 may be controlledand/or executed by the SCF 603. In a variant, the Media Control FunctionMCF 606 in the MF can send the trigger and instruct the Media DeliveryFunction MDF 607 on how to deliver the multimedia stream. In thisexample the first subscriber uses SIP to setup a multimedia session fortransmitting a first multimedia stream, whereas the second subscriberuses RTSP to receive the associated second multimedia stream.

In order for the first subscriber to invite the second subscriber toreceive the multimedia stream the following steps illustrated by theflow diagram of FIG. 7 are performed. In a first step 701 a firstsubscriber (using UE1 601) may want to share his multimedia stream witha second subscriber (using UE2 602) by setting up a SIP session with theService Control Function SCF 603 through the IMS core 604. The SIPINVITE request may comprise a list of subscriber terminal addresses, forexample using an URI-contained list, or a list may be sent to theService Control Function (SCF) outside the session, for example usingXML Configuration Access Protocol XCAP, of which an identifier may beincluded in the SIP INVITE request. Alternatively, in case of a servicesuch as Community (closed user group) TV, in which a large number ofsubscribers need to be addressed at once, the SIP INVITE request mayjust comprise a reference to the community, in the form of a Community(closed user group) Identifier, which will need to be resolved beforeproviding multiple triggers to all community subscribers.

In a second step 702 the SCF may act as a back-to-back user agent(B2BUA) and sends a session request to the Media Control Function MCF606, possibly through the IMS core. The session request to the MCFincludes information on where to receive the multimedia stream and howto distribute it. Alternatively, the SCF may use another protocoltowards the MCF such as MEGACO/H.248 or SOAP.

In a third step the MCF may send multimedia stream information to theMDF 607 to setup an RTP port and address for the first multimedia streamand associate it with a RTSP URI. The MCF may for example use SIP orMEGACO/H.248 to exchange multimedia stream information.

In a fourth step 704 the MCF response to the SCF may compriseinformation such as the address or RTP port, where the first multimediastream should be transmitted to, and/or the RTSP URI to be used by theUE2 for contacting the RTSP server functionality of the gateway.

In a fifth step 705 the SCF sends a response back to the UE1, during theexchange of first multimedia stream session information, using its SIPclient functionality

In a sixth step 706 UE1601 transmits the multimedia stream in the mannerand/or to the location indicated by the MCF.

In a seventh step 707 the SCF uses the information from the MCF toprovide a trigger to the UE2. The trigger may be a SIP contentindirection request. The request may include the RTSP URL provided bythe MF or another indication for the UE2 how to contact the gateway. Thetrigger may also be sent within an existing SIP session with the UE2, orby using a SIP REFER request.

In a eighth step 708 the invited UE2 602 initiates, in response to theSIP content indirection request, a RTSP session with the MDF (exchangeof second multimedia stream session information, 708 in FIG. 7) forreceive the multimedia content (second associated multimedia stream709). The RTSP URI may include an identifier provided in the triggermessage for the MDF to associate the RTSP session with the SIP session.The RTSP session (second associated multimedia stream) may be unicast ormulticast. When multicast is used the MF distributes the incoming(unicast) first multimedia stream of UE1 as a multicast stream. UE2 thensends, in response to the established RTSP session, an IGMP request toreceive the second associated multimedia stream.

In a ninth step the MF may send SIP NOTIFY messages to the SCF to keepthe SCF informed of the status of the RTSP session, if the SCF indicatedinterest by sending a SIP SUBSCRIBE message to the MF (not shown in FIG.7).

The invention is not limited to the embodiments described above, whichmay be varied within the scope of the accompanying claims. For instance,the term studio should not be interpreted as only meaning a professionalbroadcast studio. A studio within the meaning of this invention relatesto all systems which could provide multimedia functionality similar to astudio, e.g. a personal computer system or another multimedia systemwhich is capable of streaming live content to a user at a home locationand in response receiving user-generated content from the user.

The invention claimed is:
 1. A method, wherein a gateway is capable ofcommunicating with a first terminal and a second terminal, the methodcomprising: the gateway or the first terminal using a first protocol toexchange first media session information between the first terminal andthe gateway, wherein the exchange of the first media session informationsets up a first media stream from the first terminal; the secondterminal using a second protocol to receive a trigger provided by thegateway, wherein the trigger is to initiate an exchange of second mediasession information between the gateway and the second terminal; inresponse to receiving the trigger, the second terminal using a thirdprotocol to initiate the exchange of the second media sessioninformation between the gateway and the second terminal, wherein theexchange of the second media session information sets up a second mediastream in which the second terminal participates; and the secondterminal receiving the second media stream, wherein the second mediastream is associated with the first media stream; wherein the firstmedia stream is between the first terminal and a media server, whereinthe second media stream is between said media server and the secondterminal, and wherein said media server buffers at least part of thefirst media stream received from the first terminal before transmittingthe second media stream to the second terminal.
 2. The method accordingto claim 1, wherein the exchange of the first media session informationcomprises: the gateway providing to the first terminal at least part ofthe second media session information.
 3. The method according to claim1, wherein the exchange of the second media session informationcomprises: the gateway providing to the second terminal at least part ofthe first media session information.
 4. The method according to claim 1,wherein the exchange of the first media session information comprises:the gateway receiving, from the first terminal, an identifier of thesecond terminal.
 5. The method according to claim 4, further comprising:before using the second protocol to provide the trigger to the secondterminal, the gateway resolving the identifier of the second terminalinto a network address of the second terminal.
 6. The method accordingto claim 5, wherein providing the trigger to the second terminalcomprises the gateway transmitting the trigger to the resolved networkaddress of the second terminal.
 7. The method of claim 1, wherein thethird protocol is different from the second protocol.
 8. The method ofclaim 1, wherein the first terminal transmits the first multimediastream and the second terminal receives the second multimedia stream. 9.The method of claim 1, wherein the trigger serves to inform the secondterminal of availability of a new multimedia stream.
 10. The method ofclaim 1, wherein the first protocol is a peer-to-peer protocol.
 11. Themethod of claim 1, wherein the third protocol is a client-serverprotocol, and wherein the second receiving terminal has clientcapabilities of the third protocol and not server capabilities of thethird protocol.
 12. The method of claim 1, wherein the trigger comprisesa network address of the gateway.
 13. The method of claim 12, whereinthe network address is a URI or a URI reference.
 14. The method of claim1, wherein the first protocol and the second protocol are identical. 15.The method of claim 14, wherein the first protocol and the secondprotocol are Session Initiation Protocol (SIP).
 16. The method of claim1, wherein the gateway is configured to associate the first multimediasession information with the second multimedia session information. 17.An article of manufacture including a non-transitory computer-readablemedium, having stored thereon software instructions that, if executed bya computing device, cause the computing device to perform operationscomprising: using a first protocol to initiate an exchange of firstmedia session information between a first terminal and a gateway,wherein the exchange of the first media session information sets up afirst media stream from the first terminal; using a second protocol toprovide a trigger to a second terminal, wherein the trigger is toinitiate an exchange of second media session information between thegateway and the second terminal; using the second protocol to conductthe exchange of the second media session information between the gatewayand the second terminal, wherein the exchange of the second mediasession information sets up a second media stream in which the secondterminal participates; and using the first protocol to transmit aresponse to the first terminal, wherein the response causes the firstterminal to begin transmission of the first media stream; wherein thefirst media stream is between the first terminal and a media server,wherein the second media stream is between said media server and thesecond terminal, and wherein said media server buffers at least part ofthe first media stream received from the first terminal beforetransmitting the second media stream to the second terminal.
 18. Agateway comprising: a communication interface; and memory that storessoftware instructions that, when executed by the gateway, cause thegateway to: (i) exchange first multimedia session information with afirst terminal using a first protocol, wherein the exchange of the firstmedia session information sets up a first media stream from the firstterminal, (ii) provide a trigger to a second terminal, wherein thetrigger is provided using a second protocol, in response to which thesecond terminal is able to initiate the exchange of second multimediasession information with the gateway, and (iii) exchange secondmultimedia session information with the second terminal, using a thirdprotocol, wherein the third protocol is different from the firstprotocol, wherein the exchange of the second media session informationsets up a second media stream in which the second terminal participates;wherein the gateway further comprises a media server, wherein the firstmedia stream is between the first terminal and said media server,wherein the second media stream is between said media server and thesecond terminal, and wherein said media server buffers at least part ofthe first media stream received from the first terminal beforetransmitting the second media stream to the second terminal.
 19. Thegateway of claim 18, wherein the gateway is configured to connect to afirst terminal supporting a first protocol and to a second terminalsupporting a second protocol, wherein the first protocol is SessionInitiation Protocol (SIP) and the second protocol is Real Time StreamingProtocol (RTSP), wherein the first terminal is an originating SIP clientof a user at a user side, wherein the gateway acts as a terminating SIPclient, wherein the gateway is configured to confirm that the gateway isable to receive a multimedia session from the user and to provide thefirst terminal with multimedia session information, wherein the secondterminal is an RTSP client, wherein the gateway acts as an RTSP serveron behalf of the user, wherein the second terminal uses RTSP for sessioncontrol, and wherein the gateway is configured to inform the secondterminal that an incoming session is pending and notify the RTSP clientto connect to an RTSP server function of the gateway.
 20. The gateway ofclaim 18, wherein the gateway is configured to transmit a notificationmessage to the second terminal in response to an invitation of the firstterminal, in order to activate the second terminal to set up the secondmultimedia session between the second terminal and the gateway.
 21. Thegateway of claim 18, wherein the gateway is embedded in an IPMulti-Media Subsystem (IMS) network architecture, wherein the firstprotocol is Session Initiation Protocol (SIP), wherein the thirdprotocol is Real Time Streaming Protocol (RTSP), the IMS networkarchitecture comprising a service-control-function component and amedia-function component, wherein the memory of the gateway isdistributed in the IMS network architecture, such that: exchanging thefirst multimedia session information is handled by theservice-control-function component within the IMS network architecture;triggering the second terminal is controlled by theservice-control-function component within the IMS network architecture;and exchanging second multimedia session information is handled by themedia-function component within the IMS network architecture.
 22. Thegateway of claim 18, wherein the gateway is configured to associate thefirst multimedia session information and the second multimedia sessioninformation with each other.
 23. The gateway of claim 18, wherein thegateway further comprises Session Initiation Protocol (SIP) clientfunctionality and Real Time Streaming Protocol (RTSP) serverfunctionality.